The chemistry of particulate matter from the south Indian and Antarctic oceans

Abstract

Abstract Particulate matter was collected from the surface water of the southwest Indian Ocean and the Antarctic Ocean in the area of Kerguelen, Heard, and Crozet islands. Some deep samples were taken around Kerguelen. The samples were analysed for C, N, P, Al, Si, Ca, and Mg. In the tropical and subtropical Indian Ocean, characterized by warm, nutrient-poor surface water, C, N, and P are low and the ratios C/N/P approach those of average phytoplankton. The values of particulate Si, Al, Ca, and Mg also are low but higher near Amsterdam Island and in the north part of the study area. In the subantarctic zone, between the Subtropical and Antarctic convergences, C, N, P, and Si are, on an average, three times more abundant than in the Indian Ocean, but the C/N/P ratios are the same. South of the Antarctic Convergence or Polar Front, particulate Si becomes very abundant, especially near the Polar Front and east of Kerguelen Island. C and N also are very high at these locations but elsewhere are lower than in the subantarctic zone. The particle composition is variable but N stays in constant ratio to C. Particles are richer in P than in oligotrophic areas. In particulate matter from deep waters the C/N ratio remains constant with depth whereas C/P increases. Suspended matter below 1000 m contains an average of 57% silica. The particulate Si and C results show that the annual production of opal by organisms as determined by Lisitzin is probably too high. A budget for silica in surface water of the Antarctic Ocean is outlined.